Initial alignment

Before you can do the alignment described above you will need to get beam back through the differential interferometer (DI) head. This may be necessary, when you first install a mirror and it is tilted so much, that beam is not reflect back into the opening of the DI. It won't be, before adjusting this, that the second beam on the mirror will appear. Once you accomplished that, you can begin with the fine alignment of the mirror as described.